Hermetic high frequency module and method for producing the same

ABSTRACT

The invention relates to a high frequency module with a hollow conductor structure, consisting of a housing bottom and a housing lid, preferably consisting of ceramic. The housing bottom and the housing lid are preferably coordinated with each other in terms of their expansion characteristics. The adjusting device is mounted on the housing lid for positioning on the housing bottom, and consists of a raised photosensitive resist part which tapers conically starting from the housing lid. The adjusting device engages with the hollow conductor on assembly. The layer thickness of the adjusting device is approximately 100 to 200 μm. The housing bottom and the housing lid are permanently interconnected by soldering, preferably using solders which are introduced galvanically in solder deposits. To this end, the solder is either applied locally to the housing lid surface or introduced in vias which are structured in the lid.

This application claims the priority of German patent document 100 31407.4, filed Jun. 28, 2000 (PCT International Application No.PCT/DE01/02117, filed Jun. 6, 2001), the disclosure of which isexpressly incorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a high frequency module having a waveguidestructure, and to a method for producing such a module. Themillimeter-wave communication modules according to the inventionoperate, for example, in the GHz range and are used for the transmissionof data in traffic engineering.

For producing metal-ceramic composite structures for waveguideuncouplings in millimeter-wave communication modules, the antennasubstrates are soldered on waveguide throughfeeds in microwave housingswith a hermetic closure. In currently available manufacturing processes,so-called preforms are used for a hermetic closure which are inserted asintermediate layers between the ceramic cover and the housing. Importantcriteria for the quality of such connections are their stability withrespect to changing temperatures and their reliability in the continuousoperation. In addition, the exclusion of moisture from the housinginterior plays an important role with respect to the electricaloperation.

International Patent Document WO 91/209699 discloses a hermetic closureof ceramic-metallic housings for integrated circuits, in which ceramichousing covers are mounted and soldered by means of gold/tin preforms.Soldering is performed at a temperature below 400° C. by means of aheating electrode which is in contact with the housing. The cover andthe housing are pressed on one another during the soldering operation.

A significant disadvantage of previous manufacturing processes is thelow positioning tolerance for joining individual modules, which makesautomated manufacture more difficult, or even impossible. Theconstruction of waveguide uncouplings using preforms and theregistration pins normally used for precise positioning of the housingcover, increases the time required, and is acceptable only in the caseof small piece numbers.

One object of the invention is to provide a manufacturing process and ahigh frequency module with increased positioning tolerances in theautomated production of hermetic HF modules.

This and other objects and advantages are achieved by the waveguidearrangement according to the invention, which includes a high-frequencymodule with a waveguide structure consisting of a housing bottom and ahousing cover, preferably made of ceramics. The expansion behavior ofthe housing bottom and the cover are coordinated with one another. Forexample, the housing cover will consist of aluminum oxide and thehousing bottom will consist of Mo30Cu. An adjusting device is mounted onthe housing cover for positioning on the housing bottom. In order toprevent corrosion, the metallic housing is modified by means of a nickeland gold layer.

The adjusting device consists of a photosensitive resist elevationwhich, starting from the cover surface of the housing, tapers conically.During the mounting, the adjusting device engages in the waveguide. Thelayer thickness of the adjusting device amounts to approximately 100 to200 μm. The housing cover and the housing bottom are firmly connectedwith one another by soldering. For this purpose, solders are preferablyused which are galvanically fed into solder depots. The solder is eitherapplied locally to the housing cover surface, which is in contact withthe housing bottom, or is fed into ducts that are structured in thecover.

The method according to the invention, for producing a high-frequencymodule, includes the following steps:

-   -   The contact surface of the housing cover is structured with the        housing bottom with a first photo resist mask for a galvanic        metal deposition;    -   a gold/tin layer sequence of the solder depot is deposited;    -   the first photo resist mask is removed;    -   a second photo resist mask is structured as the adjusting        device;    -   the tin surface is cleaned of oxide;    -   the housing cover is centered on the waveguide and fixed;    -   the housing cover is soldered to the housing bottom;    -   the resist of the adjusting device is removed in a wet-chemical        manner.

The resist of the adjusting device is preferably removed in awet-chemical process, using a heated potassium hydroxide solution.

A special advantage of the invention is in its simplicity in the case ofa manual construction of waveguide throughfeeds. It also permitsautomatic assembly of the modules for a manufacturing of larger piecenumbers.

Another advantage consists of the cost-effective integration of themanufacturing steps in the manufacturing of thin-layer substrates, whichconstitutes a significant simplification of the assembling process.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a high-frequency module with a waveguidestructure;

FIG. 2 is a top view of the adjusting device; and

FIG. 3 is a view of the housing cover with the adjusting device and thesolder depot.

DETAILED DESCRIPTION OF THE DRAWINGS

An embodiment of the invention according to FIG. 1 illustrates ahigh-frequency module with a waveguide structure, consisting of ahousing bottom 1 and a housing cover 3 made of ceramics. An adjustingdevice 4 for the positioning in the waveguide on the housing bottom 1 isapplied to the housing cover 3.

For centering and fixing on the waveguide throughfeed, the adjustingdevice 4 has a photosensitive resist elevation which tapersfrustoconically starting from the housing cover 3 (FIG. 2). Duringmounting, the upper conical surface of the adjusting device 4 engages inthe waveguide 5. It is guided along the lateral surface 42 to the basesurface 41 and is centered with a low bearing force in the waveguide.The dimensions of the base surface 41 are coordinated in a preciselyfitting manner to the dimension of the waveguide.

The layer thickness of the adjusting device 4 amounts to approximately100 to 200 μm. To achieve such layer thicknesses, normally two or threecoating films of approximately 70 μm thickness are applied on top of oneanother. The edge steepness of the lateral surfaces 42 is adjusted bymeans of the exposure parameters during the photolithographic process.The housing cover and the housing bottom 1 are fixedly connected withone another by means of solders 2 which are galvanically fed locallyinto solder depots 21.

The method of producing a high-frequency module according to theinvention eliminates the need for use of a preform. The contact surfaceof the housing cover 3 is structured with the housing bottom 1 by meansof a first photosensitive resist mask for a galvanic depositing ofmetal. The gold/tin layer sequence of the solder depot used for thispurpose is deposited such that its respective thicknesses areapproximately adapted to the proportions of the eutectic alloy. A layerthickness ratio of the Au:Sn layers of approximately 1.5:1 is preferablysought, and the solder depots 21 are filled thereby (FIG. 3). Therespective layer thicknesses are in the range of between 12 μm Au/8 μmSn to 9 μm Au/6 μm Sn.

After the filling of the solder depots 21, the first photo sensitiveresist mask is removed again. A second photo sensitive resist mask isthen structured as the adjusting device 4. The mask normally consists ofa photolithographically structured coating film. The oxide surface ofthe tin is removed in a hydrogen vacuum reflow furnace at a temperatureof approximately 300° C. and a process time of several minutes. Inanother process step, the housing cover 3 is centered on the waveguide 5and fixed.

The housing cover 3 is firmly connected with the housing bottom 1 bysoldering without any fluxing agent, using, for example, an AuSnsoldering in a hydrogen atmosphere. The soldering process is alsocarried out in a hydrogen vacuum reflow furnace preferably while usingthe eutectic solder material of an approximate composition of 80% byvolume Au and 20% by volume Sn. The melting point of the eutecticcompound is approximately 280° C. The soldering process of the furnaceoperated in a reducing hydrogen atmosphere in connection with nitrogenas a protective gas is carried out at a temperature of approximately320° C. for a duration of several minutes. The used gold and tin layer,which is deposited on the soldering side of the substrate in depots,and, in the course of the tempering process, results in a completemixing of the Au/Sn layers while forming a homogeneous structure,replaces the otherwise used preforms.

The resist of the adjusting device 4 is removed in a wet-chemical mannerpreferably by means of a heated potassium hydroxide solution. For thispurpose, the module is immersed for approximately 10 minutes in a 50%potassium hydroxide solution at a temperature of 70° C.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

1. High-frequency module with a waveguide structure, comprising: ahousing bottom; a housing cover; and an adjusting device mounted on thehousing cover, for positioning the housing cover on the housing bottom;wherein the adjusting device comprises a photosensitive resistelevation.
 2. The high-frequency module according to claim 1, whereinthe adjusting device conically tapers starting from the housing cover.3. High-frequency module with a waveguide structure, comprising: ahousing bottom; a housing cover; and an adjusting device mounted on thehousing cover, for positioning the housing cover on the housing bottom;wherein the housing cover and the housing bottom are fixedly connectedwith one another by solders.
 4. The high-frequency module according toclaim 3, wherein galvanic solders are galvanically fed into solderdepots.
 5. The high-frequency module according to claim 1, wherein thehousing cover is made of ceramics.
 6. The high-frequency moduleaccording to claim 1, wherein the adjusting device engages in thewaveguide.
 7. The high-frequency module according to claim 1, wherein alayer thickness of the adjusting device is approximately 100 to 200 μm.8. A method of producing a high-frequency module having a housing coverwith solder depots and a housing bottom said method comprising:structuring the contact surface of the housing cover with the housingbottom with a first photo resist mask for a galvanic metal deposition;depositing a gold/tin layer sequence of the solder depot; removing thefirst photo resist mask; structuring a second photo resist mask as theadjusting device; cleaning the tin surface of oxide; centering andfixing the housing cover on the waveguide; soldering the housing coverto the housing bottom; and removing the resist of the adjusting devicein a wet-chemical manner.
 9. The method according to claim 8, whereinthe step of removing the resist of the adjusting device is performedusing a heated potassium hydroxide solution.